The implicit threat model here is "no one outside your machine can do something to you to make 127.0.0.1 traffic route elsewhere." It's true that software running on your machine can make copies of things and send them elsewhere, but that's not the point of the sentence you quoted.
This is definitely false, without any routing tables. Any unprivileged user can start an SSH tunnel listening on any localhost port above 1024, sending traffic out to wherever.